A Broadband Squeezed Light Source for Table-Top Interferometry

TL;DR

This paper characterizes a broadband squeezed light source for quantum interferometry, achieving up to 8.6 dB of squeezing over 100 MHz, suitable for space-time fluctuation measurements.

Contribution

It presents the development and characterization of the broadest-linewidth squeezed light source for long-term quantum interferometry applications.

Findings

Achieved up to 6.8 dB of squeezing directly measured.

Maintained at least 3 dB of squeezing across 100 MHz bandwidth.

Inferred squeezing level increased to 8.6 dB after dark noise correction.

Abstract

We report on the characterisation of one of two broadband squeezed light sources developed for the Quantum Enhanced Space-Time (QUEST) experiment, using balanced homodyne detection. QUEST consists of a pair of co-located, table-top, power-recycled Michelson interferometers designed to probe stationary space-time fluctuations. The interferometers are designed to be shot-noise limited in the frequency range from 1 to 200 MHz, and squeezed light will be employed with the goal to reduce the shot noise by 6 dB at frequencies inside the linewidth of the optical parametric amplifier (OPA). We directly observed up to 6.8 dB of squeezing and maintained at least 3 dB of squeezing across the full 100 MHz measurement bandwidth. After accounting for the dark noise contribution, the inferred squeezing level increased to 8.6 dB. Our squeezed light source is based on a hemilithic OPA with a 43.6 mm round-trip optical length and a linewidth of 138 MHz, making it the broadest-linewidth device to date among those suitable for long-term operation.